1. Field of the Invention
The present invention relates generally to blowing agent compositions, and more particularly the use of said compositions in non-polyisocyanate-based foams.
2. Description of the Prior Art
The use of blowing agents in the production of cellular plastics is well established. Plastics in cellular form have a number of advantages over non-expanded materials, especially with respect to cost, weight reduction and insulating ability.
In the past, two types of blowing agents have been employed in virtually all cellular plastics production. The first type consists of low boiling inert liquids that evaporate under the exotherm of polymer formation or upon the release of pressure during processing at elevated temperature. Examples of such low boiling inert liquids include butane, pentane and trichlorofluoromethane. These hydrocarbon blowing agents are highly flammable, and are also undesirable due to their classification as photochemically reactive volatile organic compounds (VOCs) which contribute to photochemical smog.
The second type of blowing agents includes those that are formed by a chemical reaction or by thermal decomposition of a compound. An example of the former is the formation of CO.sub.2 from the reaction of water and isocyanate in the production of flexible polyurethane foam, while an example of the latter is the decomposition of azidocarbonamide to form nitrogen, which is employed to expand vinyl chloride, low density polyethylene, and a number of other polymers.
Historically, chlorofluorocarbons (CFCs) such as dichlorodifluoromethane (CFC-12) and trichlorofluoromethane (CFC-11) have been employed as the blowing agents of choice for polymeric foams. However, such completely halogenated molecules have been implicated in the destruction of stratospheric ozone, and due to their high ozone depletion potential (ODP), CFCs, including CFC-11 and CFC-12, are slated for phase-out by the end of the century.
Hydrochlorofluorocarbons (HCFCs) such as 1,1-dichloro-1-fluoroethane (HCFC-123) which contain at least one hydrogen atom are less damaging to stratospheric ozone in comparison to the CFCs. However, as indicated above, although these blowing agents have ODPs of zero they are highly flammable, and are also less desirable due to their classification as photochemically reactive volatile organic compounds which contribute to photochemical smog.
An additional problem associated with the use of certain blowing agents is that of compatibility of the blowing agent composition with the additional components of the foam blowing system. Applications requiring multi-component liquid systems must form stable solutions in order to produce homogeneous foams. Efforts to incorporate some blowing agents of the prior art have resulted in the separation of components and poor cell structure in the expanded foam.
A need therefore exists for novel blowing agents which are non-toxic, nonflammable, compatible with system components and environmentally acceptable. The present invention addresses that need.